In general, a polyimide resin refers to a resin having an imide group in the backbone, which is a high heat-resistant resin manufactured by condensation polymerization of aromatic tetracarboxylic acid or the derivatives thereof with aromatic diamine, or aromatic diisocyanate followed by imidization. The resin is widely used in film, print panel, electric wire enamel, etc.
Further, the polyimide resin can have a variety of molecular structures depending on the types of the monomers therein. As for the aromatic tetracarboxylic acid constituent, pyromellitic dianhydride (PMDA) or biphenyltetracarboxylic dianhydride (BPDA) is used. As for the aromatic diamine constituent, oxydianiline (ODA) or p-phenylene diamine (p-PDA) is used for condensation polymerization. The typical polyimide resin has a repetitive unit of the following formula 1: ##STR2##
The polyimide resin with the formula 1 as a repetitive unit is high heat-resistant, insoluble, and non-meltable with the following properties:
(1) excellent thermo-oxidative property;
(2) superior heat-resistance based on the utilization at high temperature, i.e., 260.degree. C. for a long-term use, and 480.degree. C. for a short-term use;
(3) excellent electrochemical and mechanical properties;
(4) excellent radiation resistance and low temperature properties;
(5) intrinsic non-combustible properties; and
(6) excellent chemical-resistant properties.
In spite of the fact that the polyimide resin with formula 1 as repetitive unit possesses an excellent heat resistance property, the processing therein is extremely difficult due to insolubility and non-melting property.
To overcome the shortcoming of the polyimide resin, several methods have been devised: a) method of introducing polar groups into the backbone or side chains of the polymer, b) method of introducing the connecting group or bulky pendant groups into the polymer, and c) method of enhancing the flexibility of the backbone of the polymer.
In particular, as part of research to enhance the solubility of the polyimide resin, T. Kurosaki et al. discloses a method of preparing a soluble polyimide using alicyclic anhydride as a monomer (Macromolecules, 1994, 27, 1117 and 1993, 26, 4961). Also, Qn Jin et al. discloses a method of preparing a soluble polyimide resin using the cyclic diamine (J.P.S. Part A. Polym. Chem. Ed., 31, 2345.about.2351).
In the present invention, the mixture of dioxotetrahydrofuryl 3-methylcyclohexene-1,2-dicarboxylic dianhydride (DOCDA), which is an alicyclic dianydride, and aromatic tetracarboxylic dianhydride, in addition to aromatic diimine compound were used to prepare a novel soluble polyimide having excellent heat-resistance, transparency and liquid crystal alignment capacity.
As such, the objectives of the invention herein lies in providing a soluble polyimide resin having a dialkyl substituent for a liquid crystal alignment and the monomer thereof; which has superior heat-resistance, transparency and liquid crystal alignment capacity. Further, the objective of the invention includes the manufacturing method of the same.